The invention relates to a control valve for an injector, having a valve body in which a valve seat is embodied, and having a control spool which is displaceably disposed in the valve body and has a valve face which cooperates with the valve seat.
One such control valve is known for instance from German Patent Disclosure DE 197 27 896 A1 and serves to bring about the opening of a valve needle in order to inject fuel into a cylinder of an internal combustion engine. To make the forces acting on the control spool of the control valve as slight as possible, force-balanced control valves are used, in which the operating medium, that is switched, which is at high pressure, exerts a total zero or only slight force on the control spool.
The control valve according to the invention has the advantage of being especially simple to assemble, even though because of the geometry of the control spool and the guide extension, a balanced control valve is realized. Although the control spool must have a larger diameter than the guide extension and the valve seat, so that reliable sealing of the valve seat is assured, problem-free assembly of the control valve is possible because of the guide bush. Several tasks can be performed simultaneously by the guide bush, such as a sealing function.
Advantageous refinements of and improvements to the control valve defined herein are possible by means of the provisions recited in the disclosure.
In a preferred embodiment, it is provided that the control spool, on its side remote from the guide extension, is provided with a centering extension, which is received displaceably in a bore in the valve body. The centering extension improves the positioning of the control spool relative to the valve seat, so that optimal tightness is assured.
It is also provided that a compression spring is disposed between the centering extension and the bottom of the bore; that an outflow bore leads away from a chamber that is embodied between the valve seat and the centering extension; and that a delivery bore discharges into a chamber that is formed between the guide bush and the valve seat. The compression spring presses the control spool away from the valve seat, so that when a suitable counter force is absent, the opening of the valve is brought about. A compact overall design is obtained by means of the disposition of the outflow bore and the delivery bore.
Furthermore, an actuator can be provided, which can act on the guide extension via a hydraulic step-up chamber. The hydraulic step-up chamber makes it possible for the actuating force of the actuator and its actuation stroke to be converted into values that are suitable for actuating the control spool. The requisite adaptation can be attained in a simple way through the choice of a suitable cross-sectional ratio between the cross section of the guide extension and the cross section of an actuating piston of the actuator.
Preferably, the hydraulic step-up chamber communicates with the delivery bore. This can be attained for instance by means of a slight leakage flow between the guide extension and the guide bush. In this way, no separate supply for the hydraulic step-up chamber is needed.
The actuator can be a piezoelectric actuator. An actuator of this kind can be triggered with only very slight power.
According to a preferred embodiment of the invention, the valve body is embodied in two parts, and the guide bush is provided with a collar that provides sealing between the two parts of the valve body. In this version, the guide bush is automatically fixed between the two parts of the valve body without requiring a separate fastener. Also, the guide bush can be used to assure the sealing of the hydraulic step-up chamber.
The invention will be better understood and further objects and advantages thereof will become more apparent from the ensuing detailed description of a preferred embodiment taken in conjunction with the drawing.